Rubber products typified by crosslinked rubber, when, for instance, used in rolls or packing, often require those with low hardness. In order to maintain low hardness and properties, the composition needs to be considered carefully.
Meanwhile, rubber products including crosslinked rubber are processed in a kneading apparatus so that materials such as rubber, filler and softener are mixed evenly, after which crosslinking is performed by adding crosslinking agents and crosslinking aids. In this case, it may not be possible to knead a large amount of materials if a kneading apparatus is overloaded, which consequently undermines productivity.
An attempt was made to lower the kneading load by pouring oil used for extender oil in order to obtain rubber product with low hardness (Background Art of Patent Literature 1).